Hydra attenuata, a freshwater coelenterate, has the ability to regenerate its entire form from a fragment of body tissue, without the necessity of cell division or DNA synthesis. The cells change their fates and take part in the formation of a new pattern, which is regulated to fit into the reduced tissue. There are seveal aspects of the pattern formation process which will be examined using grafting, transplantation, and regeneration experiments. The roles of inhibition as the "inhibitor" of an autocatalytic patterning reaction, and the size sensor which limits the reaction so as to maintain proportions will be reevaluated. The specific source of inhibition in the head, and the mechanism of transmission will be examined. The kinetics of proprotioning in the head structures and in the bsal disc will be followed during regeneration to determine if they are consistent with the kinetics of inhibition return. The ability of inhibition to modulate proportions when at a high level will also be determined. The interactions between the head and foot during simultaneous regeneration will be examined to determine if there is a single patterning system of both or two separate systems which cross-react. Finally, the possibility of an adhesivity gradient in the body column, which is a force in its shapin, will be considered.